A voltage-controlled oscillator (VCO) is a device typically used in phase-locked loop (PLL) circuits to provide an output clock signal that is phase locked to a reference clock signal. The VCO has an output frequency that can be adjusted by varying a control voltage input. The voltage-to-frequency gain of the VCO specifies an amount of frequency change that results from a given change in the control voltage input. The voltage-to-frequency gain, also referred to interchangeably herein as tuning slope, is typically represented by the symbol “Kv” and expressed in units of Hz/V.
In higher performance VCOs, it may be useful to have lower gain while maintaining wide frequency coverage. In order to accomplish this, a VCO frequency coverage range may be divided into several sub-bands, where each sub-band covers part of the whole range. A VCO with the VCO frequency coverage range divided into several sub-bands may be referred to interchangeably herein as a multi-band VCO. A sub-band of the several sub-bands may be selected before a PLL locks the multi-band VCO to the reference clock signal.